Charles Sheffield - Aftermath

Wilmer released the sheet of paper with the diagram, and it hovered before him in the free-fall environment of the Schiaparelli’s cabin. “That’s a general comment, but it’s easy to catalog specific effects. First, there will be only a small change at ground level. The atmosphere has expanded, but its total mass remains constant. The surface will experience the same atmospheric pressure, because the whole column of air above it exerts the same downward force.

“But now think about conditions higher up. The atmosphere still becomes thinner with height, but it does so more slowly than it used to. So if you go high enough, the air is more dense than it was at that same height before Supernova Alpha. The drag force and frictional heating on a spacecraft will increase — and they have an exponential dependence on air density.

“The routines that we put into Lewis came from the general software library applicable to our class of orbiters. They provide an explicit calculation for drag force as a function of height, in terms of spacecraft angle of attack, mass, shape, and velocity — and air density. But it’s the air density at a given height as it was before Supernova Alpha — not as it is now — that’s in the equations. An acceptable angle of attack for a ship fifty miles up, moving through the atmosphere as it was two months ago, would be an absolute disaster today. No orbiter could stand the increased drag and heating. We saw what it did to the Lewis .”

Wilmer had credibility and authority on all matters scientific. He also spoke as though what he said was no more than common sense, and quite undeniable. Celine reminded herself that it was the unquestioned acceptance of authority — Zoe’s authority, as head of the expedition — which had led her to remain silent before. She could not afford to do it again.

“You may be right, Wilmer. But you may be wrong.” And when he stared at her in surprise — this wasn’t the old Celine — she went on, “Jenny may be right, there was an error in the way the software was transferred, so Zoe’s action drove the controls the wrong way. Or Reza could be right, it was pilot error on Zoe’s part that destroyed the Lewis. The trouble is, we have no way of knowing which idea is correct. Even if you are right, there’s nothing we can do to prove it.”

“Oh, but there is.” One nice thing about Wilmer, he was too intellectually secure to become upset when he was questioned. He rubbed at the top of his head and went on, “We lost radio telemetry for the critical period, but we have a complete visual record from the Schiaparelli’s big scope. That provides our observables. We can compute trajectories using a variety of different assumptions — that the angle of attack was adjusted the wrong way, or that it was reduced but the drag was already too high for that to help, or any other idea that anyone has. The right model is the one which minimizes residuals between computer and observed values. We can even use the difference between computed and observed data to calculate a density function for today’s atmosphere, one that best matches a computed orbit to the observations. I’m sure Jenny can handle that.”

“Jenny?” Celine looked uncertainly to Jenny Kopal.

“Easily.” Jenny nodded. She seemed like a woman reprieved from a death sentence. “It’s a nonlinear least squares fitting problem, but we have all the routines.”

“So let’s do it.” Celine was about to add, Soon, so we can get out of here and down to Earth. But she was learning. “Take as much time as you need. You tell me when you’re done. Then we’ll discuss what comes next.”

• • •

You could force patience on yourself and everyone else, but no one said you had to like it.

Celine watched Jenny working for a few minutes, with Wilmer sitting by to assist if and when needed. Then she left the control cabin and wandered away to the Schiaparelli’s observation chamber. She had another mystery to ponder.

Zoe had been the leader of the Mars expedition. Ludwig Holter had been second in command. No backup to those two had ever been mentioned. Oversight, or deliberate act by the selection committee?

Now Zoe and Ludwig were dead. And Celine, without making any conscious decision, seemed to have taken over the direction of the surviving group. Did she want to do that? Or, inverting the question, did she have any choice?

Celine stared out at Earth, its surface again shrouded in night. The radio silence continued, broken only by weak and sporadic signals that addressed purely local problems of food, water, and power supply. The old Earth had been a celestial beacon, a roar of radio and television signals easily picked up when the Schiaparelli was orbiting Mars. That had gone. The firefly glow of light from the big cities was no longer visible. In its place she saw the ruddy sparks of bush fires across much of sub-Saharan Africa.

The planet to which she so much wanted to return was nothing like the world that they had left. If they survived to land on it, they would find a tougher, wilder place.

First, though, they had to live through the descent. Who would make the crucial decisions in the hours ahead? Put like that, the question of leadership became clear. She did not trust Wilmer or Jenny to direct the group. She wasn’t sure she trusted Reza to do much at all, he was showing increasing signs of strangeness. And there was no one else.

Celine left the observation chamber and headed for the control room where the others were working. True, she did not wholly trust herself. But maybe Zoe Nash, for all her apparent confidence and certainty, had felt the same way.

Uneasy lies the head.

The important question wasn’t whether or not you thought you were the right one to lead. It was whether others believed you were.

What am I? What is my function?

Celine, squeezed into the improvised hammock between Wilmer and Jenny and facing away from the front of the orbiter, felt a new wave of uncertainty rising within her. Reza sat behind them at the controls. Celine didn’t like that, but she had no choice. He was by far the best pilot. She could see his distorted image in the shiny rear panel, singing to himself. Unless she told him to abort in the next sixty seconds, the Clark would leave the safe haven of ISS-2 and begin reentry.

She had performed none of the data analysis and modeling that proved Wilmer’s assertion was correct. That work had been done by Jenny and by Wilmer himself. It showed that the crew of the Lewis had died not because of pilot ineptitude or software transfer error, but because the equations embedded in the control programs no longer modeled correctly the atmosphere of today’s Earth.

She had not changed the software, to incorporate the parameters of the new atmosphere determined by the data analysis. That had been Jenny’s work.

Nor would she fly the Clark back home. That responsibility lay with Reza, now well into manic mood.

What, then, did she do?

She worried, when apparently no one else did. The others were completely confident that the problem that killed Zoe and the rest of the Lewis crew had been solved. As Reza cheerfully said, “Everything else was on the button, exactly the way it should have been. We’ve cleared up the only problem.” Yet it was his partner,

Jenny, who in another context had assured the group that test a program as you liked, it always had one bug left. And she and Reza apparently didn’t realize that “program” was a general term, applying just as well to a return from orbit as to a computer subroutine.

Celine wondered how much longer she would have delayed the attempt to return to Earth, without Reza’s remark the previous day: “The log shows this orbiter’s past due for maintenance. There’s a steady deterioration in condition, even when it’s not being used.”